1. Field of the Invention
The present invention relates to a susceptor supporting construction used for attaching a susceptor to a chamber.
2. Prior Art Statement
In a semiconductor manufacturing application and so on, as shown, for example, in FIG. 6, it is necessary to attach a ceramic susceptor 2 to an inner wall surface of a chamber 10. In order to achieve such an attachment, one end 21a of a tubular supporting member 21 made of ceramics is attached to a contacting surface (rear surface) 2b of the ceramic susceptor 2, and the other end 21c of the supporting member 21 is attached to an inner wall surface 10d of the chamber 10. The supporting member is formed by heat resistive ceramics such as alumina, aluminum nitride and so on. An inner space 6 of the supporting member 21 is communicated with an opening 10a of the chamber 10. A portion between the supporting member 21 and the chamber 10 is sealed in an airtight manner by using an O-ring 20. In this manner, a portion between the inner space 6 of the supporting member 21 and an inner space 5 of the chamber 10 can be sealed in an airtight manner, so that a gas in the inner space 5 of the chamber 10 is not leaked outside of the chamber 10. In the ceramic susceptor 2, for example, a resistant heating member 4 is embedded.
A temperature of a mount surface (heating surface) 2a of the ceramic susceptor 2 for mounting a semiconductor wafer 1 reaches to a temperature for example, not less than 400° C. and sometimes not less than 600° C. On the other hand, a sealing member made of rubber such as the O-ring 20 and so on is unendurable for high temperatures, and a heat-resistant temperature of the sealing member is normally about 200° C. Therefore, it is preferred to control a temperature near the O-ring 20 to be not more than 200° C. by cooling a portion near the O-ring 20 by means of a cooling flange 8 arranged in the chamber 10.
However, in this embodiment, a temperature of the ceramic susceptor 2 becomes high as mentioned above, and a temperature of the one end 21a of the supporting member 21 exceeds for example 400° C., while a temperature of the other end 21c of the supporting member 21 is cooled to not more than 200° C. In this case, a temperature gradient in an inner portion of the supporting member becomes not less than 200° C.
In order to improve a connection strength of the supporting member with respect to the susceptor and to arrange gas holes and through holes for passing a terminal or a thermocouple in a wall surface of the supporting member 21, it is necessary to make a thickness of the supporting member 21 more thicker so as to increase a contacting area of the supporting member 21 with respect to the susceptor. However, if the supporting member becomes thicker, a heat conduction amount propagated through the supporting member becomes larger due to a temperature gradient in the supporting member mentioned above. As a result, a cold spot is generated to the heating surface 2a by a heat conduction increase near the connecting portion (one end) 21a of the supporting member. Therefore, it is effective to make a main portion of the supporting member thin and to arrange a thick extending portion (flange portion) to the supporting member at which a side end portion of the susceptor is faced.
However, if such a thick flange portion is arranged to an end portion of the supporting member, in the case that the susceptor is heated to high temperatures, there is a tendency such that an inner stress concentrated at near the boundary between the main portion and the flange portion becomes excessive. Therefore, in order to prevent a failure of the supporting member, it is necessary to set an upper limit temperature of the susceptor.